The present invention relates to a developer dispensing apparatus for a developer station in a xerographic printing machine and, more particularly, to an apparatus which utilizes a helical spring as an auger mechanism.
In prior art printing machines, the toner material used to develop a latent image formed on a photoreceptor surface is consumed in a development process and must be periodically replaced within the development system in order to sustain continuous operation of the machine. One technique which has become generally accepted is the use of a separate toner or developer hopper with a dispensing mechanism for adding the toner from the hopper to the developer apparatus on a regular, or as needed, basis.
The 1065.TM. machine a product of the Xerox.TM. corporation uses a helical spring or as it has come to be known a slinky auger as in a toner dispenser or replenisher. One end of the slinky auger in that machine is attached to a motor shaft and is driven thereby. The connection between the motor shaft and auger is effected by inserting the auger attachment leg through a hole in the motor shaft. Thus, the slinky auger is not rigidly attached to the drive shaft nor is its center in any way restrained from moving off center. This method of attachment works well for the movement of toner particles only. An example of such an attachment is depicted in U.S. Pat. No. 4,943,830 granted to Timothy J. Sulenski on Jul. 24, 1990.
In an arrangement for replenishing developer material which comprises not only toner particles but carrier beads, the aforementioned method of attachment of the auger to the drive mechanism is inadequate. With such an arrangement, rotation of the slinky auger tends to cause segregation of the toner and carrier beads. The carrier beads, being the heavier of the two components, settle to the bottom or floor of the dispenser. Thus, a new "apparent" floor is created which causes the individual coils of the slinky auger to ride up on the carrier beads and eventually end up above the desired home position, home position being defined as the position where the auger coils are closely adjacent and parallel to the sump floor. As the build-up of carrier beads continues, the slinky auger attachment leg slides or shifts within the hole of the shaft motor. This causes the slinky auger to be driven off its center of rotation causing the coils to physically interfere with the side walls of the sump. Eventually, the auger jams and locks up into the wall and starts wrapping itself about the auger motor shaft thereby leading to failure of the dispenser either through stalling of the dispenser motor caused by torque variations or through breakage of the auger.
Unwanted movement of the free end of such an auger and a solution therefor is addressed in the '830 patent but the undesired movement of the driven end is not.